Semicondutor Integrated Circuit Device

ABSTRACT

A semiconductor integrated circuit device including an I/O circuitry capable of low-voltage high-speed operation at low cost is provided. In the I/O circuitry, when an I/O voltage (for example, 3.3 V) is lowered to a predetermined voltage (for example, 1.8 V), portions causing a speed deterioration are a level conversion unit and a pre-buffer unit for driving a main large-sized buffer. In view of this, a high voltage is applied to a level up converter and a pre-buffer circuit. By doing so, it is possible to achieve an I/O circuitry capable of low-voltage high-speed operation at low cost.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationNo. JP 2005-120605 filed on Apr. 19, 2005, the content of which ishereby incorporated by reference into this application.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a semiconductor integrated circuitdevice. More particularly, it relates to a technology effectivelyapplied to a semiconductor integrated circuit device such as a systemLSI or a microprocessor for mobile devices.

BACKGROUND OF THE INVENTION

The inventors of the present invention have studied the followingtechnologies regarding a semiconductor integrated circuit device such asa system LSI or a microprocessor for mobile devices.

In recent mobile devices, I/O (input/output) voltages have been more andmore diversified in order to achieve the reduction in voltage for lowerpower consumption and also to use the conventional interface thatoperates at a high voltage for effectively utilizing the existingresources. With respect to the voltage reduction, in particular, demandsfor the lower power consumption have been strong in an interface unit ofa dynamic random access memory (DRAM), which is a general-purposestorage element. Such demands serve as an engine of standardization oflow-voltage I/O. For example, in mobile devices, the voltage of 1.8 Vwhich is lower in comparison with the current industry standard of 3.3 Vhas been becoming the standard interface voltage for SDRAM, DDR-SDRAM,and others.

On the other hand, it is also important to keep the conventionalinterface. This is because a removable non-volatile memory (such asflash memory) is designed to operate at a high voltage (3.3 V), and itsinterface specifications are also standardized in the industry. Such aconventional interface has been adopted to various types of devices ofdifferent product generations, and has an advantage of cost reduction bya mass-production effect. Therefore, demands for the continued use ofsuch a conventional I/O are also high.

Therefore, at present, in consideration of cost and power reduction, itis extremely difficult to unify all power supply voltages for I/Ocircuitries (input/output circuitry) incorporated in an LSI (forexample, to unify all power supply voltages into a voltage of 1.8 V).

Meanwhile, for low-voltage (1.8 V) I/O, a high-speed operation has notbeen much demanded so far. Thus, for 1.8 V I/O, a transistor supposed tobe operated at a standard voltage (for example, 3.3 V) can be used asbeing operated at a low voltage (1.8 V). However, recent mobile devicesare better equipped with a variety of applications, and needs fortransferring a large amount of data at high speed have been increasing.Therefore, demands for a high-speed operation have been increasing evenin I/O of a low-voltage operation. In the future, speeding up of 1.8 VI/O will be imperative.

SUMMARY OF THE INVENTION

Meanwhile, as a result of the study by the inventors of the presentinvention for the technologies as described above, the following hasbeen revealed.

SoC (System-on-a-Chip) LSIs which are currently in the mainstream aresupposed to be operated at a core voltage (for example, 1.2 V), which isa supply voltage for transistors forming a logic circuit such as a CPU,and at an I/O voltage (for example, 3.3 V) for matching with externaldevices. Thus, two types of thickness are designed for the gateinsulating film of the MISFET. When 1.8 V I/O is designed under aboundary condition in such a design as described above, a MISFET for 3.3V is used for the 1.8 V operation. In this case, as is evident from aso-called current-voltage relationship of the MISFET in which asaturation current Ids of the MISFET is proportional to the square of adifference between a gate voltage Vg and a threshold voltage Vth(Ids∝(Vg−Vth)²), a saturation current in the 3.3 V operation isapproximately six times larger than a saturation current in the 1.8 Voperation, where it is assumed that Vth=0.7 V. In terms of a delay time(Tpd), the delay time is a quotient obtained by dividing a product of apower supply voltage V and a gate capacitance C by Ids (Tpd≈×V/Ids).Therefore, the operation is slowed about three times. For this reason, ahigh-speed operation at 1.8 V is difficult to achieve by using atransistor for 3.3 V.

In order to increase the speed of the 1.8 V operation, the design inwhich a MISFET for 3.3 V is formed by using a MISFET with a lowthreshold value obtained by adding an implantation process may bepossible. However, if MISFETs with a low threshold value are used forthe entire low-power I/O circuitry extending from a level conversioncircuit to a pre-buffer and a main buffer, the amount of leakage currentis increased, and the low-power characteristic which is imperative formobile devices is lost.

Alternatively, the design in which I/O operating at 1.8 V is formed byusing a MISFET for a logic circuit operating at 1.2 V may be possible.An example thereof is disclosed in U.S. Pat. No. 5,969,542 (PatentDocument 1). This patent document 1 discloses that 2.5 V I/O is formedby using a 1.8 V device, in which a withstand voltage mitigationtechnology for mitigating a maximum applied voltage to the MISFET isused. However, if I/O circuitry for 1.8 V is formed by the use of aMISFET for 1.2 V by applying the technology described above, thethreshold value of the MISFET for 1.2 V has to be set low due to aso-called scaling law. Therefore, a problem of an increase in leakagecurrent occurs. Furthermore, since a measure for electrostatic damage(ESD measure) has to be newly implemented, an additional number ofprocesses and cost increase are inevitable.

The above-described examples have a small impact on the LSImanufacturing process and the number of masks. However, if noconsideration is required at all for these factors, it is possible totake a method of using a plurality of MISFETs having different gateinsulating film thicknesses. When a MISFET designed to have a gateinsulating film thickness that can obtain a large current at 1.8 V isused, since the ON current of the MISFET is proportional to the inverseof the gate insulating film, if such a special MISFET can be added,speeding-up can be achieved. In this case, a leakage current does notpose any problem. However, since three types of gate insulating filmthicknesses have to be provided, it is unavoidable to increasecomplexity of the manufacturing process, the number of masks, and thenumber of processes for quality control. Consequently, the manufacturingcost is increased.

Consumer products including mobile devices are cost-conscious productsto win the competition with other companies. Therefore, it is desired tonarrow down the types of devices for manufacturing a SoC LSI, reduce thenumber of masks to be used, and simplify the process steps. Thus, as theI/O circuitry for mobile devices, it is necessary to design the 1.8-Vhigh-speed I/O by using transistors for 3.3 V at low cost.

Therefore, an object of the present invention is to provide asemiconductor integrated circuit device with an I/O circuitry capable oflow-voltage high-speed operation at low cost.

The above and other objects and novel characteristics of the presentinvention will be apparent from the description of this specificationand the accompanying drawings.

The typical ones of the inventions disclosed in this application will bebriefly described as follows.

In the present invention, in view of the fact that it is a levelconversion unit and a pre-buffer unit for driving a main large-sizebuffer that cause a speed degradation when an I/O voltage vcc is loweredin an I/O circuitry, a high voltage is applied to these units. By doingso, it is possible to achieve the low-voltage high-speed operation I/Oat low cost.

More specifically, a semiconductor integrated circuit device accordingto the present invention comprises: a circuit operating at a first powersupply voltage; and an output circuit operating at a second power supplyvoltage higher than the first power supply voltage, wherein thesemiconductor integrated circuit device further comprises: means whichonce amplifies a signal voltage amplitude to a third power supplyvoltage higher than the second power supply voltage, and then performsconversion to a signal having an amplitude of the second power supplyvoltage at the time of signal transmission from the circuit operating atthe first power supply voltage to the output circuit operating at thesecond power supply voltage.

The effects obtained by typical aspects of the present invention will bebriefly described below.

That is, in a semiconductor integrated circuit device with an I/Ocircuitry, low-voltage high-speed operation can be achieved at low cost.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a block diagram showing a main structure of a semiconductorintegrated circuit device according to one embodiment of the presentinvention;

FIG. 2A is a diagram depicting a structure example of I/O circuitry atan output side in the semiconductor integrated circuit device accordingto one embodiment of the present embodiment;

FIG. 2B is a diagram depicting a structure example of I/O circuitry atan output side in the semiconductor integrated circuit device accordingto one embodiment of the present embodiment;

FIG. 3 is a waveform diagram showing the operation of the I/O circuitryat the output side in FIG. 2;

FIG. 4 is a drawing showing structure examples of transistors (MISFETs)for use in the semiconductor integrated circuit device according to oneembodiment of the present embodiment;

FIG. 5 is a drawing of a layout example of the I/O circuitry in FIG. 2and a cross-sectional structure thereof;

FIG. 6 is a drawing of another layout example of the I/O circuitry ofFIG. 2 and a cross-sectional structure thereof;

FIG. 7A is a drawing depicting another structure example of the I/Ocircuitry at the output side in the semiconductor integrated circuitdevice according to one embodiment of the present embodiment;

FIG. 7B is a drawing depicting another structure example of the I/Ocircuitry at the output side in the semiconductor integrated circuitdevice according to one embodiment of the present embodiment;

FIG. 8 is a drawing of another structure example of the main buffershown in FIG. 7;

FIG. 9 is a drawing of a layout example of the I/O circuitry in FIG. 7and a cross-sectional structure thereof;

FIG. 10A is a block diagram showing one example of a power supplyconnection structure in the semiconductor integrated circuit deviceaccording to one embodiment of the present invention;

FIG. 10B is a block diagram showing another example of a power supplyconnection structure in the semiconductor integrated circuit deviceaccording to one embodiment of the present invention;

FIG. 11 is a drawing of one example of a power supply connectionstructure on a package in the semiconductor integrated circuit deviceaccording to one embodiment of the present invention;

FIG. 12 is a block diagram of a structure example when the presentinvention is applied to a semiconductor integrated circuit device havinga plurality of I/O power supplies;

FIG. 13 is a block diagram of another structure example when the presentinvention is applied to a semiconductor integrated circuit device havinga plurality of I/O power supplies;

FIG. 14 is a circuit diagram of a structure example of an I/O circuitry(withstand voltage mitigation circuit) of FIG. 13;

FIG. 15 is a waveform diagram showing the operation of the I/O circuitryof FIG. 14;

FIG. 16 is a circuit diagram of a structure example of a levelconversion circuit in the semiconductor integrated circuit deviceaccording to one embodiment of the present invention;

FIG. 17 is a block diagram of a structure example of an input circuitwhen the present invention is applied to SSTL2;

FIG. 18 is a circuit diagram of a structure example of a differentialamplifier of FIG. 17;

FIG. 19 is a circuit diagram of another structure example of thedifferential amplifier of FIG. 17;

FIG. 20 is a waveform diagram showing the operation of the input circuitof FIG. 17; and

FIG. 21 is a block diagram showing a structure example of a terminatingtransistor of the input circuit in the semiconductor integrated circuitdevice according to one embodiment of the present invention.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. Note that componentshaving the same function are denoted by the same reference symbolsthroughout the drawings for describing the embodiment, and therepetitive description thereof will be omitted.

FIG. 1 is a drawing of a main structure of a semiconductor integratedcircuit device according to one embodiment of the present invention. Thefeature of the present embodiment lies in that, in an output buffer forsending a signal from a logic circuit in an LSI (semiconductorintegrated circuit device) to the outside thereof, the signal is firstconverted to a signal with a voltage amplitude higher than that of apower supply voltage for use in an interface unit, and is then convertedto a power supply voltage amplitude for the interface.

FIG. 1 depicts an LSI supplied with a power supply voltage vdd (forexample, at 1.2 V, which is referred to as a first power supply voltage)for use in a logic circuit (logic unit) LGC such as a CPU in the LSI, apower supply voltage vcc (for example, at 3.3 V, which is referred to asa third power supply voltage) for standard interface, and a power supplyvoltage vcc_18 (for example, at 1.8 V, which is referred to as a secondpower supply voltage) for low-voltage interface. This block diagramdepicts the state where an interface signal of 1.8 V is inputted to theLSI, processed through internal logics, and then outputted from the LSI.The signal inputted from an input pad PAD_I is delivered to an internallogic circuit LGC through an input buffer IBF and a signal levelconversion circuit (level down converter LDC) for conversion from an I/O(input/output) voltage (1.8 V) to the power supply voltage vdd of thelogic circuit.

On the other hand, the signal level of the signal from the logic circuitLGC to the outside has to be converted to a signal level of the powersupply voltage vcc_18 for I/O from the power supply voltage vdd of thelogic circuit. At this time, as a feature of the present invention,after the signal amplitude is once amplified by a level up converter LUCto the vcc level which is a higher voltage, the resultant signal isamplified by a pre-buffer PBF, and then converted to an interfacevoltage vcc_18 in a main buffer MBF at the last stage for delivery. Inthis manner, the level conversion unit and the pre-buffer unit operationspeed is degraded can be operated at high speed. Therefore, alow-voltage high-speed operation is possible even by the use of ahigh-withstand-voltage MISFET. The level conversion circuit used herecan be achieved by using, for example, a level conversion circuitdisclosed in Japanese. Patent Application Laid-Open Publication No.2003-152096 (Patent Document 2).

Also, the level up converter LUC can be shared between the I/O for lowvoltage vcc_18 and the I/O for high voltage vcc, which makes itunnecessary to re-design the level conversion circuit. Therefore, aneffect of reducing the number of design steps can be achieved. The levelup converter disclosed in Patent Document 2 is a circuit for rapidlyconverting the signal amplitude of a low voltage (1 V or lower) to ahigh-voltage (3.3 V) amplitude, but it has a little complex structure.Therefore, if the level up converter can be shared by all I/Ocircuitries (all input/output circuitries), an effect of reducing designcost can be achieved.

Meanwhile, in the present embodiment, when the signal amplitude isconverted from a vdd power supply voltage level to vcc_18 power supplyvoltage level, the signal amplitude is increased by the level conversioncircuit and the pre-buffer and then driven. Therefore, there is aconcern about an increase in power consumption. However, in a generalI/O circuitry, since the load for driving the I/O circuitry is extremelylarge in comparison with the gate capacitance of an internal transistor,it does not cause any problem. For example, an external output load CLis defined in the specifications as 15 pF, which is extremely large. Onthe other hand, the gate width of the I/O circuitry is at most about 100μm, and its capacitance is about several hundreds of fF. Therefore, itis evident that dominant power consumption is the power to charge anddischarge the load capacitance CL by the main buffer MBF at the laststage and the power consumption in the level up converter LUC and thepre-buffer PBF is at a level that is negligible.

The leakage current is also at a level that is negligible. The reason isas follows. Since the leakage current tends to be proportional to adrain-source voltage, the leakage current is increased in comparisonwith a leakage current at the time of application of 1.8 V. However,since the high-withstand-voltage MISFET inherently has a high thresholdvalue, in view of the leakage current on the entire SoC chip, theleakage current becomes an amount that is negligible.

Furthermore, another feature of the present embodiment lies in that,since the level up converter and the pre-buffer are shared by thelow-voltage I/O circuitry and the high-voltage I/O circuitry, thestructure of the level up converter and the pre-buffer which determinethe characteristics of the I/O circuitry can be determined almostindependently of the voltage at the last stage. Thus, coarse adjustmentand some fine adjustment of the characteristics can be achieved onlywith one type of voltage specification (for example, 3V, which is avoltage value allowing a 10% decrease as a future margin in the case ofa high voltage of 3.3 V). For this reason, another effect of attainingstable performance with short TAT and at low cost can be achieved.

Therefore, according to the semiconductor integrated circuit device ofthe present embodiment, the operation speed of 1.8 V I/O can beincreased by driving the level conversion unit and the pre-buffer unitat a high voltage.

Also, the level conversion unit and the pre-buffer unit can be shared by3.3 V I/O and 1.8 V I/O. Further, when the applied voltage of 3.3 V isused in common, the shared use of components and extraction of cellcharacteristics can be easily attained.

In FIG. 1, the ground potential of the input circuit and the groundpotential of the level conversion circuit of the output circuit areequal to that of the internal logic circuit, that is, vss. This isbecause, since the main buffer MBF of the output circuit is formed of anextremely large transistor, when the transistor is turned ON and OFF,the ground potential vssc of the main buffer MBF and the pre-buffer PBFof the output circuit may include a large noise. By preventing suchnoise from being included in the input circuit and the level conversioncircuit, effects of mitigating degradation in operation speed, improvingsignal quality, and the like can be achieved. Note that, if such asituation would not occur in a product, the ground potential vssc forI/O can be used for designing the input circuit and the level conversioncircuit.

Next, the structure of an I/O circuitry OIOC at the output side will bedescribed. FIG. 2 shows the structure of an I/O circuitry OIOC at theoutput side, in which FIG. 2A schematically depicts the I/O circuitryOIOC at the output side and FIG. 2B depicts a power supply for eachterminal of a transistor of the I/O circuitry OIOC.

First, the general outline of the I/O circuitry OIOC at the output sidewill be described with reference to FIG. 2A. The level up converter LUCis a circuit having a function to increase a signal amplitude, and isoperated by applying a vdd power supply voltage for use in the internallogic circuit and a vcc power supply voltage with a high potential. Thepre-buffer PBF is driven at the high voltage vcc.

The main buffer MBF at the last stage is driven at the vcc_18 powersupply voltage, which is an interface power supply voltage. FIG. 2A andFIG. 2B depict the case where a P type MISFET has a substrate terminalconnected to vcc and a source terminal connected to vcc_18, as oneexample of the structure of this main buffer MBF. Also, in this example,a threshold voltage of the P type MISFET is set low.

Although not shown, in the case where a MISFET with a low thresholdvalue is not used as the P type MISFET of the main buffer MBF, a gatewidth W is set wide so as to secure a driving current of this P typeMISFET.

However, in a normal process, an analog transistor that handles mixedsignals is set in many cases, and in most cases, such a transistor isformed of a MISFET with a low threshold voltage. Therefore, when such aMISFET is used, a high-speed low-voltage I/O circuitry can be realizedwithout increasing the number of process steps or the number of masks.For this reason, an embodiment using such a MISFET is mainly describedhere.

FIG. 2B is a circuit diagram of the pre-buffer PBF and the main bufferMBF shown in FIG. 2A. Although I/O circuitry is generally complexbecause it includes an enable signal, a driving magnification switchingsignal, and others, I/O circuitry will be described here as an inverterserving as the simplest amplifying circuit. The present invention canalso be applied to the I/O circuitry having a complex function otherthan the inverter.

The pre-buffer PBF is formed of a MISFET to which vcc is supposed to beapplied, and its threshold voltage is designed as a standard circuitryto which vcc is supplied.

On the other hand, a MISFET similar to that of the pre-buffer is usedfor an N type MISFET of the main buffer MBF. However, a MISFET with areduced threshold voltage, which is obtained by changing theimplantation for a channel of a MISFET, is used for a P type MISFET.Since a potential of a substrate electrode VB is vcc and a potential ofa source electrode VS is vcc_18 in this P type MISFET, a substrate biaseffect occurs. Also, since the operating voltage of the precedingpre-buffer PBF is vcc, the output thereof becomes a high output state atthe vcc level. Therefore, on condition that the P type MISFET of themain buffer MBF is turned OFF (when the gate voltage of the P typeMISFET is vcc), a so-called negative gate voltage effect (since the Ptype MISFET is used in this case, a gate voltage is higher than thesource voltage, and it is strongly turned OFF) works together with thesubstrate bias effect, and thus, it is possible to reduce the leakage.

FIG. 3 is an operating waveform diagram of the I/O circuitry at theoutput side shown in FIG. 2. The case where an output node nd1 from theinternal logic circuit LGC has an amplitude of a vdd voltage and makes atransition at a time T1 from a low level (vss level) to a high level(vdd level) will be described. It is hereinafter defined that atransition is made at the time when the amplitude of the signal becomeshalf. The signal from the node nd1 is then inputted to the level upconverter LUC, where the signal amplitude is converted to a vcc level.Due to the delay time of the level up converter, an output node nd2 ofthe level up converter makes a transition at a time T2 from a low level(vssc level) to a high level (vcc level). In this example, since abuffer-type level up converter is assumed, the logic of the node nd1 andthat of the node nd2 match with each other. However, when aninverter-type level up converter is used, a similar signal levelconversion is performed except that the logic is inverted. Then, thesignal from the node nd2 is inputted to the pre-buffer PBF, where adriving force is amplified to a driving force sufficient to drive themain buffer MBF. Since the pre-buffer PBF is operated also at the vccpower supply voltage, the signal amplitude at an output node nd3 of thepre-buffer PBF is equal to the amplitude of the vcc power supply voltageat the node nd2. In this example, in consideration of the amount ofdelay in the pre-buffer PBF, a transition is made at a time T3 from alow level (vssc level) to a high level (vcc level). Then, the signalfrom the node nd3 is inputted to the main buffer MBF, and the mainbuffer MBF drives an external high load through an output pad PAD_O.Since the main buffer MBF is driven at the vcc_18 power supply voltage,the amplitude at an output node nd4 is equal to the amplitude of thevcc_18 power supply voltage. Also, this example depicts the case of anobtuse output waveform of the main buffer MBF due to a large externalload, and a transition is made at a time T4 from a low level (vssclevel) to a high level (vcc_18 level).

Next, the case where a transition is made at a time T5 from a high level(vdd level) to a low level (vss) will be described. The signal from thenode nd1 is then inputted to the level up converter LUC, where thesignal amplitude is converted to a vcc level. Due to the delay time ofthe level up converter, the output node nd2 of the level up convertermakes a transition at a time T6 from a high level (vcc level) to a lowlevel (vssc level). In this example, since a buffer-type level upconverter is assumed, the logic of the node nd1 and that of the node nd2match with each other. However, when an inverter-type level up converteris used, a similar signal level conversion is performed except that thelogic is inverted. Then, the signal from the node nd2 is inputted to thepre-buffer PBF, where a driving force is amplified to a driving forcesufficient to drive the main buffer MBF. Since the pre-buffer PBF isoperated also at the vcc power supply voltage, the signal amplitude atthe output node nd3 of the pre-buffer PBF is equal to the amplitude ofthe vcc power supply voltage at the node nd2. In this example, inconsideration of the amount of delay in the pre-buffer PBF, a transitionis made at a time T7 from a high level (vcc level) to a low level (vssclevel). Then, the signal from the node nd3 is inputted to the mainbuffer MBF, and the main buffer MBF drives an external high load throughthe output pad PAD_O. Since the main buffer MBF is driven at the vcc_18power supply voltage, the amplitude at the output node nd4 is equal tothe amplitude of the vcc_18 power supply voltage. Also, this exampledepicts the case of an obtuse output waveform of the main buffer MBF dueto a large external load, and a transition is made at a time T8 from ahigh level (vcc_18 level) to a low level (vssc level).

FIG. 4 is a drawing that depicts examples of the MISFETs for use in thepresent embodiment together with their cross-sectional views. In FIG. 4,VG denotes a gate electrode, VD denotes a drain electrode, VS denotes asource electrode, and VB denotes a substrate electrode. In this drawing,MISFETs having a thin gate insulating film whose gate electrode issymbolized by a line and MISFETs having a thick gate insulating filmwhose gate electrode is symbolized by a rectangular box are shown, inwhich they are classified according to whether the type is an N type ora P type and according to the magnitude of the threshold voltage.

The gate insulating film thickness of the MISFET for use in the internallogic circuit is designed to be about 2 nm, and the MISFET having athick gate insulating film thickness for use in the I/O circuitry isdesigned to have the gate insulating film thickness larger than that ofthe MISFET for use in the internal logic circuit, that is, have the gateinsulating film thickness about 6 to 7 nm, for example.

A TNS-NMISFET is an N type MISFET with a thin-film standard thresholdvoltage for use in the internal logic circuit, and a TNS-PMISFET is a Ptype MISFET with a thin-film standard threshold voltage.

A TNL-NMISFET is an N type MISFET with a thin-film low threshold voltagefor use in the internal logic circuit, and a TNL-PMISFET is a P typeMISFET with a thin-film low threshold voltage.

A TCS-NMISFET is an N type MISFET with a thick-film standard thresholdvoltage for use in the I/O circuitry, and a TCS-PMISFET is a P typeMISFET with a thick-film standard threshold voltage.

A TCL-NMISFET is an N type MISFET with a thick-film low thresholdvoltage for use in the I/O circuitry, and a TCL-PMISFET is a P typeMISFET with a thick-film low threshold voltage.

This example shows the transistors having a so-called triple wellstructure, in which a deep N well DNW is formed on a P typesemiconductor substrate P-sub and then an N well NW for forming a P typeMISFET and a P well PW for forming an N type MISFET are formed on thedeep N well DNW. Alternatively, a double well structure, which has onlythe N well NW and the P well PW without using the deep N well DNW, isalso possible. In the low-threshold-voltage MISFET, the thresholdvoltage of the MISFET is reduced by providing additional implantationfor a channel portion of the transistor. An N type diffusion layer NLcorresponds to a diffusion layer implanted area of the N type MISFET anda diffusion layer implanted area for substrate power supply of the Ptype MISFET, and a P type diffusion layer PL corresponds to a diffusionlayer implanted area of the P type MISFET and a diffusion layerimplanted area for substrate power supply of the N type MISFET.

FIG. 5 depicts a layout example of the I/O circuitry. In this layoutexample, the I/O circuitry at the output side shown in FIG. 2 isassumed, and a layout area is broadly divided into four areas. In thiscase, a conceptual plan view of the layout is shown in a lower portionof the drawing, and a cross-sectional view thereof taken along A-A′ ofthe plan view is shown in an upper portion thereof. For the purpose ofsimplification, FIG. 5 depicts an example in which each area has twocells laid out in a back-to-back manner (two sets of an N type MISFETand a P type MISFET). In an actual layout, the size of each area can bedefined in accordance with the restrictions on a vertical direction anda horizontal direction, and the layout may be achieved with a differentnumber of sets other than the number of sets shown in the drawing.

A first area AREA1 is an area to which vdd, which is a power supplyvoltage for the internal logic circuit, is applied, and is supplied withvdd and vss power supply voltages.

A second area AREA2 is an area to which vcc is applied, and is suppliedwith vcc and vssc power supply voltages.

A third area AREA3 is an area to which vcc_18 is applied, and issupplied with vcc_18 and vssc power supply voltages.

A fourth area AREA4 is a well separation area for electricallyseparating the first area and the second and third areas. When thedouble well structure is used, this fourth area can be narrowed. Whenthe ground level power supply voltage vssc of the second and third areasis equal to the ground level power supply voltage vss of the first area,an LSI can be formed even without a deep N well DNW. Since substrateseparation between vcc and vdd can be achieved only with the P well PW,no well separation area is required. However, since such a deep N wellDNW is effective for noise separation, by separating power supplies ofthe first area and the second and third areas where power supply noiseis heaviest, the effect of, for example, increasing the noise immunitycan be obtained.

In the first area, a control logic of the I/O circuitry and a vddapplying unit for a level up converter and a level down converter arelaid out. In the second area, a vcc applying unit for the level upconverter and a pre-buffer are laid out. In the third area, a vcc_18applying unit for the level down converter, a main buffer, and an ESDprotective element are laid out.

In the third area AREA3 to which vcc_18 is applied, a substrate powersupply is different from the power supply of the P type MISFET of themain buffer MBF. Therefore, the third area AREA3 is partially differentfrom the second area AREA2 in layout. In this example, since powersupply wiring in a cell is assumed to be formed with a metal firstlayer, one vcc power supply line and two vcc_18 power supply lines areused for layout. Since the vcc power supply supplies power only to thesubstrate of the P type MISFET, the amount of current supply can besmaller in comparison with vcc_18. Therefore, only a thin metal wiringis sufficient in this layout.

Next, the cross-sectional structure will be described. In the upperportion of FIG. 5, the cross section taken along A-A′ shown in thedrawing is schematically depicted. The structure depicted here is thecase of a so-called triple well structure, in which the deep N well DNWis formed in the P type semiconductor substrate P-sub and then the Nwell NW for the P type MISFET and the P well PW for the N type MISFETare formed on the deep N well DNW, thereby forming a MISFET. Thetransistor for the internal logic circuit is formed of a MISFET with athin gate insulating film, and this MISFET uses polysilicon poly12 as agate electrode. The transistor for I/O is formed of a MISFET with athick gate insulating film, and this MISFET uses polysilicon poly33 as agate electrode. Power supply to the substrate and source of eachtransistor is performed by using a metal first layer M1. Power issupplied to the substrate and source from the metal first layer M1through a contact CT. In this case, only power supply to the substrateis shown, but power supply to the source electrode of the MISFET isperformed similarly through a method known to those skilled in the art.

FIG. 6 depicts a modification example of the layout depicted in FIG. 5,showing an embodiment in which two-layer metal wiring is used for powersupply wiring. FIG. 6 also depicts a cross section taken along B-B′.Similar to FIG. 5, the metal first layer M1 is used to form power supplywiring. In addition, a metal zeroth layer M0 is used to strengthen thepower supply. As described above, when two-layer power supply wiring isused, power supply to the substrate can be performed through the wiringof the metal zeroth layer M0, and the power supply to the source of theMISFET can be performed through the wiring of the metal first layer M1,which makes it possible to achieve the effects of area reduction, wiringflexibility improvement, and others. In the example shown in FIG. 6,different wiring layers are used for the wiring of the substrate andthat of the source electrode of the P type MISFET of the main bufferMBF.

As is evident from FIG. 6, in this layout, only two power supply linesof the metal first layer are required for each cell. In a portion towhich vcc_18 is applied, as shown in the cross-sectional view, nocontact CT is provided between the metal first layer M1 and the metalzeroth layer M0 in order to separate the vcc_18 power supply and the vccpower supply. Other power supplies have a contact CT connected betweenthe metal first layer M1 and the metal zeroth layer M0. Theimplementation of such a layout achieves effects of the flexibilityincrease in wiring of the metal first layer M1 and simplification of thelayout.

FIG. 7 is a drawing of another embodiment of the present invention.Similar to FIG. 2, FIG. 7 depicts an example of the I/O circuitry at theoutput side. FIG. 7A schematically depicts the I/O circuitry at theoutput side, and FIG. 7B depicts a power supply of each terminal of atransistor of the I/O circuitry.

First, the general outline of the I/O circuitry at the output side willbe described with reference to FIG. 7A. The level up converter LUC is acircuit having a function to increase a signal amplitude, and isoperated by applying a vdd power supply voltage for use in the internallogic circuit and a vcc power supply voltage with a high potential. Thepre-buffer PBF is driven at the high voltage vcc. The main buffer MBF atthe last stage is driven at the vcc_18 power supply voltage, which is aninterface power supply voltage. Different from FIG. 2A and FIG. 2B, FIG.7A and FIG. 7B depict one example of the structure of the main bufferMBF, in which a substrate electrode VB of a P type MISFET is connectedto vcc_18 and the P type MISFET is formed of a MISFET with a standardthreshold voltage.

FIG. 7B is a circuit diagram of the pre-buffer PBF and the main bufferMBF shown in FIG. 7A. Although I/O circuitry is generally complexbecause it includes an enable signal, a driving magnification switchingsignal, and others, I/O circuitry will be described here as an inverterserving as the simplest amplifying circuit. The present invention canalso be applied to the I/O circuitry having a complex function otherthan the inverter. The pre-buffer PBF is formed of a MISFET to which vccis supposed to be applied, and its threshold voltage is designed as astandard circuitry to which vcc is supplied. On the other hand, a MISFETsimilar to that of the pre-buffer PBF is used for an N type MISFET ofthe main buffer MBF. Since a potential of a substrate electrode is vccand a potential of a source electrode VS is vcc_18 in this P typeMISFET, on condition that the P type MISFET is turned OFF (when the gatevoltage of the P type MISFET is vcc), the leakage can be reduced due tothe negative gate voltage effect.

FIG. 8 depicts another embodiment of the main buffer MBF. A feature ofthis case lies in that a MISFET with a reduced threshold voltage is usedas the P type MISFET of the main buffer shown in FIG. 7. Accordingly,since the driving force of the P type MISFET is increased, a pull-up ofthe output node becomes faster. As a result, the operation speed of theI/O circuitry at the output side can be increased.

Although not shown, making a gate length LG of the MISFET short will beeffective in speed-up. This is because the current of the MISFET isapproximately proportional to an inverse of the gate length.

FIG. 9 depicts a layout example of the structure of FIG. 7. In thislayout example, the I/O circuitry at the output side shown in FIG. 7Aand FIG. 7B is assumed, and a layout area is broadly divided into fiveareas. In this case, a conceptual plan view of the layout is shown in alower portion of the drawing, and a cross-sectional view thereof takenalong C-C′ in the plan view is shown in an upper portion thereof. Forthe purpose of simplification, FIG. 9 depicts an example in which eacharea has two cells laid out in a back-to-back manner (two sets of an Ntype MISFET and a P type MISFET). In an actual layout, the size of eacharea can be defined in accordance with the restrictions on a verticaldirection and a horizontal direction, and the layout may be achievedwith a different number of sets other than the number of sets shown inthe drawing. These five areas are classified by the substrate powersupply of the MISFET.

A first area AREA1 is an area to which vdd, which is a power supplyvoltage for the internal logic circuit, is applied, and is supplied withvdd and vss power supply voltages. A second area AREA2 is an area towhich vcc is applied, and is supplied with vcc and vssc power supplyvoltages. A third area AREA3 is an area to which vcc_18 is applied, andis supplied with vcc_18 and vssc power supply voltages. A fourth areaAREA4 is a well separation area for electrically separating the firstarea and the second and third areas. A fifth area AREA5 is a wellseparation area for electrically separating the second area and thethird area. This is because, since the substrate potential of the P typeMISFET of the main buffer MBF is different from the substrate potentialof the P type MISFET of the pre-buffer PBF and the level up converterLUC, substrate insulation is required between the main buffer MBF andthe pre-buffer PBF.

The size of these fourth and fifth areas can be reduced when a doublewell structure is used. This is because, since the fifth area can formthe substrate separation of vcc and vcc_18 by only the P well PW if thedeep N well DNW is not set, separation of the deep N well DNW is notnecessary. It is unnecessary to set this deep N well DNW when the groundlevel power supply voltage vssc of the second and third areas is equalto the ground level power supply voltage vss of the first area. However,since such a deep N well DNW is effective for noise separation, byseparating power supplies of the first area and the second and thirdareas where power supply noise is heaviest, the effect of, for example,increasing the noise immunity can be obtained.

In this example, the case where power supply wiring is formed with themetal first layer M1 has been described. However, the wiring using thetwo or more metal wiring layers in which a metal zeroth layer M0 and ametal first layer M1 are used is also possible as shown in FIG. 6. Inthis case, effects of simplification of the layout and the areareduction can be achieved.

FIG. 10A and FIG. 10B are drawings that depict a power supply structure(power supply allocation) of an LSI to which the present invention isapplied. FIG. 10A and FIG. 10B each depict a structure example includinga vdd power supply, vcc1 power supply, a vcc2 power supply, and a vcc_18power supply. For example, the vdd power supply is 1.2 V, vcc1 is 2.5V,vcc2 is 3.3 V, and vcc_18 is 1.8 V. Note that a ground level powersupply is omitted. FIG. 10A depicts a state where vcc2 and vcc_18 aresupplied to an input/output circuitry SDRAMIF for SDRAM, and FIG. 10Bdepicts a state where vcc1 and vcc_18 are supplied to the input/outputcircuitry SDRAMIF for SDRAM. The input buffer IBF, the pre-buffer PBF,the main buffer MBF, and other components shown in FIG. 1 are providedin the input/output circuitry SDRAMIF.

First, circuit blocks using the vdd power supply include a logic unitLogic such as a CPU and an SRAM which is an on-chip storage element. Aplurality of such units and elements may be integrated. Furthermore,although not shown, these circuits may be operated at a different powersupply voltage (for example, vdd2=0.9 V) as long as the voltage is belowthe withstand voltage of the MISFET. Circuit blocks using vcc1 includean analog circuit ANLG and input/output circuitries IFC1 and IFC2 forflash memories, which are off-chip storage elements, and others. A vcc2power supply voltage is supplied to a standby circuit STBYC, whichcontrols the chip even when the chip enters a standby state and acircuit block to which vdd is applied is cut off by an off-chip oron-chip power supply switch, and to control circuits PSWC1 and PSWC2 foran on-chip power supply cut-off switch. Circuit blocks using the vcc_18power supply include the input/output circuitry SDRAMIF for the SDRAM,which is an external storage element. A voltage higher than vcc_18 issupplied to this SDRAMIF. In FIG. 10A, vcc2 which is the highest voltageof all is used. Depending on the specifications, even when vcc1 is usedas shown in FIG. 10B, the speeding-up effect can be achieved althoughthe operation is slower in comparison with the case of using vcc2.

In many cases, MISFETs forming the analog circuit ANLG, the input/outputcircuitries IFC1 and IFC2 for the flash memories and others, the standbycircuit STBYC, the control circuits PSWC1 and PSWC2 for power supplycut-off switch, and the input/output circuitry SDRAMIF for the SDRAMhave a thick gate insulating film. Also, the thickness of the gateinsulating films thereof has the same design value. This achieves aneffect of reducing manufacturing cost.

FIG. 11 is a conceptual drawing of a connection of I/O circuitries foran LSI and power supply terminals. In FIG. 11, ball-grid-type powersupply wiring is shown, in which power supplies are taken from the uppersurface of the LSI chip. With the progress of miniaturization inmanufacturing process, a method in which power supplies inside the LSIare directly bonded from the upper surface of the chip so as to avoid avoltage drop has become dominant. At this time, if vcc_18, vssc, and vccpower supplies are arranged on the upper portion of the chip near 1.8 VI/O circuitry driven at a low voltage, it is possible to achieve thehighest power supply performance and to simplify the layout. In FIG. 11,the ball grid arrangement is implemented so that vss and vdd are evenlyarranged. Depending on the LSI, however, power consumption is notuniform in some cases. In such a case, it is preferable to arrange theball grids for power supply so that large power can be given to thecircuit blocks that consume an electric current most.

FIG. 12 depicts another embodiment of the I/O circuitry. In this case,three types of I/O circuitry are shown. For the purpose ofsimplification, only an output system from an internal logic circuitCLGC to the outside of the chip is shown. Each of the I/O circuitries isan I/O circuitry IO18C operated at the lowest voltage (for example, 1.8V), an I/O circuitry IO33C operated at the highest voltage (for example,3.3 V), and an I/O circuitry IO25C operated at an intermediate voltagetherebetween (for example 2.5 V).

The I/O circuitry IO33C has operating voltages of vdd and vcc and theirground levels of vss and vssc. Also, the I/O circuitry IO33C has aprotective element ESD1 for protecting the inside of the LSI fromexternal static and others.

The I/O circuitry IO25C has operating voltages of vdd and vcc_25 andtheir ground levels of vss and vssc. Also, the I/O circuitry IO25C hasthe protective element ESD1 for protecting the inside of the LSI fromexternal static and others.

The I/O circuitry IO18C has operating voltages of vdd and vcc_18 andtheir ground levels of vss and vssc. Also, the I/O circuitry IO18C hasthe protective element ESD1 for protecting the inside of the LSI fromexternal static and others. Note that the I/O circuitry shown in FIG. 1corresponds to the I/O circuitry IO18C.

The MISFETs which form these I/O circuitries include two types. One isthe MISFET having a thin gate insulating film and designed to operate ata vdd power supply voltage, and the other is the MISFET having a thickgate insulating film and designed to operate at a vcc power supplyvoltage.

All protective elements ESD1 are formed of the same circuits. Forexample, a MISFET operating at vcc is used as an active element.

By adopting such a circuit, protective elements can be used in common,and an effect of reducing design cost can be achieved.

FIG. 13 is a modification example of FIG. 12, that is, anotherembodiment of the I/O circuitry. In this case, three types of I/Ocircuitry are shown. For the purpose of simplification, only an outputsystem from the internal logic circuit CLGC to the outside of the chipis shown. Each of the I/O circuitries is an I/O circuitry IO18C2operated at the lowest voltage (for example, 1.8 V), an I/O circuitryIO33C2 operated at the highest voltage (for example, 3.3 V), and an I/Ocircuitry IO25C2 operated at an intermediate voltage therebetween (forexample, 2.5 V).

The I/O circuitry IO33C2 has operating voltages of vdd, vcc, and vcc_25and their ground levels of vss and vssc. Different from IO33C shown inFIG. 12, this circuitry has a MISFET formed based on the assumption thatit is operated by a vcc_25 power supply. Such a MISFET to be operated byvcc_25 has a feature that its gate insulating film is thinner than thatof a MISFET supposed to be operated at vcc. Therefore, higher-speedoperation at a lower voltage (for example, 2.5 V) is possible incomparison with the case where the circuitry is formed by using a MISFETfor vcc. However, if a vcc power supply voltage is directly applied tooperate this MISFET supposed to be operated by vcc_25, the voltageexceeds the withstand voltage of the gate insulating film, and theMISFET is destroyed. Also, the I/O circuitry IO33C2 has a protectiveelement ESD2 for protecting the inside of the LSI from external staticand others. Different from ESD1, this ESD2 uses a MISFET operated atvcc_25 as an active element. However, if a vcc power supply voltage isdirectly applied to operate this MISFET supposed to be operated atvcc_25, the gate insulating film is destroyed. For its prevention, acircuitry measure for suppressing a maximum applied voltage is requiredfor this ESD2 circuit.

The I/O circuitry IO25C2 has operating voltages of vdd and vcc_25 andtheir ground levels of vss and vssc. This circuitry is similar to IO25Cshown in FIG. 12, but the gate insulating film of the MISFET to whichvcc_25 is applied is thinner than that of the MISFET for use in IO25C.Also, the I/O circuitry 1O25C2 has a protective element ESD3 forprotecting the inside of the LSI from external static and others.Different from ESD1, this ESD3 uses a MISFET supposed to be operated atvcc_25 as an active element.

The I/O circuitry IO18C2 has operating voltages of vdd, vcc_18, andvcc_25 and their ground levels of vss and vssc. This circuitry issimilar to the I/O circuitry IO18C shown in FIG. 12, but the gateinsulating film of the MISFET to which vcc_25 and vcc_18 are applied isthinner than that of the MISFET for use in the I/O circuitry IO18C.Also, the I/O circuitry IO18C2 has the protective element ESD3 forprotecting the inside of the LSI from external static and others.Different from ESD1, this ESD3 uses a MISFET supposed to be operated atvcc_25 as an active element. Note that the I/O circuitry shown in FIG. 1corresponds to the I/O circuitry IO18C2.

The MISFETs which form these I/O circuitries include two types. One isthe MISFET having a thin gate insulating film and designed to operate ata vdd power supply voltage, and the other is the MISFET having a thickgate insulating film and designed to operate at a vcc power supplyvoltage. Furthermore, in the circuitry IO33C2, destruction of the gateinsulating film has to be prevented when using the vcc power supply forthe MISFET designed for vcc_25 power supply.

If this circuitry is used, the MISFET optimized for application of avcc_25 voltage can be used as a MISFET with a high withstand voltage.Therefore, the circuitry to which a vcc_25 power supply voltage isapplied can be operated at high speed.

FIG. 14 depicts one embodiment of the I/O circuitry IO33C2 shown in FIG.13. In FIG. 14, a level up converter LSC, a pre-buffer PBF, and a mainbuffer MBF are shown. A feature of this case lies in that a MISFEThaving a thin gate insulating film for use in an internal logic circuitand a MISFET optimized for a vcc_25 voltage for I/O are used as theMISFETs. In FIG. 14, reference characters identical to those in FIG. 4are used for description, and it is assumed that a maximum appliedvoltage for a MISFET having a thick gate insulating film is vcc_25. Byusing the MISFETs described above, a high-speed operation under a vcc_25voltage can be achieved in comparison with the case of a MISFET designedbased on the assumption that a vcc power supply voltage is applied andhaving a thicker gate insulating film.

Meanwhile, a vcc power supply voltage cannot be directly applied to thisMISFET. This is because the gate insulating film of this MISFET does nothave a sufficient thickness to endure the application of vcc. Therefore,in order to achieve the operation by the vcc power supply, the maximumapplied voltage to this MISFET has to be suppressed to the vcc_25voltage or lower. Thus, in the present embodiment, a withstand voltagemitigation mechanism described below capable of suppressing the maximumapplied voltage to the MISFET to vcc_25 is provided in order to enablethe vcc operation.

First, the connecting relation of this circuitry will be described. Aninput of the level up converter LSC is first supplied to LUC_B, where asignal having an amplitude between a vdd power supply voltage and a vsspower supply voltage is converted to a signal having an amplitudebetween a vcc_25 power supply voltage and the vss power supply voltage.This circuit outputs complementary signals nd11 and nd11 b. Outputsignals thereof are inputted to LUC_A, where they are converted tosignals having an amplitude of a vcc power supply voltage and a vddpower supply voltage. An output of LUC_A is a signal nd12 b. The outputsof LUC_A and LUC_B, that is, nd11 and nd12 are then inputted to thepre-buffer PBF. The pre-buffer PBF is composed of PBF_A and PBF_B asshown in FIG. 14. PBF_A amplifies a driving force of a signal whichmakes a transition from the power supply voltage vdd to the power supplyvoltage vcc, and PBF_B amplifies a driving force of a signal which makesa transition from the power supply voltage vssc to the power supplyvoltage vcc_25. Outputs of the pre-buffer PBF are a signal nd16 fromPBF_A and a signal nd15 from PBF_B, and they are inputted to the mainbuffer MBF.

In this case, a MISFET having a low threshold value is used for each ofMN1, MN2, MN3, MN4, MN9, MN10, MN5, and MP5. This is because, sincethese MISFETs are used for the purpose of mitigating the withstandvoltage, a gate-source voltage is low. If there is no problem even whenthe operation speed is decreased a little, these MISFETs can bereplaced, by MISFETs having a standard threshold voltage. In this case,effects of simplifying a manufacturing process and reducing the cost canbe achieved.

Next, the operation of the circuitry shown in FIG. 14 will be described.

The case where an input signal i is at a high level (vdd) will bedescribed.

At this time, in LUC_B, an output of an inverter INV1 is inputted toMISFETs MN1, MN7, MP1, and MP9, and an output of an inverter INV2receiving the output signal of the inverter INV1 is inputted to MISFETsMN2, MN8, MP2, and MP10. As a result, since nd11 becomes a low level(vss), MP7 is turned ON. Since MP9 is turned ON, nd11 b becomes a highlevel (vcc_25).

When nd11 becomes a low level (vss) and nd11 b becomes a high level(vcc_25), in LUC_A, MP3 is turned OFF, MN9 is turned ON, MP4 is turnedON, and MN10 is turned OFF. Since MP11 is turned OFF and MN3 is turnedON, nd12 becomes a low level (vdd), MP12 is turned ON, and nd12 bbecomes a high level (vcc). MP13 and MP14 are always in an ON state.These MISFETs MP13 and MP14 are used for the purpose of suppressing anelectric current, so as to make a transition to a low level at highspeed at the time of signal level conversion. MP13 and MP14 can beomitted if a desired performance can be obtained without these MISFETs.In this case, an area reduction effect can be achieved. As describedabove, the operation of the level conversion circuit is defined.

Two signals whose signal amplitude is converted by the level upconverter LSC are buffered by the pre-buffer PBF to a driving forcesufficient to drive the main buffer MBF at the last stage. At this time,since nd11 is at a low level, nd15 is at a low level (vssc). On theother hand, since nd12 is at a high level (vcc), nd16 becomes a lowlevel (vdd). These outputs from the pre-buffer PBF are inputted to themain buffer MBF. In the main buffer MBF, since nd15 is at a low level,MN16 is turned OFF and MP6 is turned ON. Therefore, since nd13 becomes avcc_25 potential and the gate potential of MN5 is vcc_25 power supplyvoltage, MN5 is also turned OFF. On the other hand, since nd16 is at alow level (vdd), MP13 is turned ON and MN6 is turned OFF. Therefore,since nd14 is becomes vcc potential and the gate potential of MP5 isvdd, MP5 is also in an ON state. Consequently, an output o is at a vcclevel.

Next, the case where the input signal i is at a low level (vss) will bedescribed.

At this time, in LUC_B, an output of the inverter INV1 is inputted tothe MISFETs MN1, MN7, MP1, and MP9, and an output of the inverter INV2receiving the output signal of the inverter INV1 is inputted to theMISFETs MN2, MN8, MP2, and MP10. As a result, since nd11 b becomes a lowlevel (vss), MP8 is turned ON and MP10 is turned ON. Thus, nd11 becomesa high level (vcc_25).

When nd11 b is at a low level (vss) and nd11 is at a high level(vcc_25), in LUC_A, MP4 is turned OFF, MN10 is turned ON, MP3 is turnedON, and MN9 is turned OFF. As a result, MP12 is turned OFF. Since MN4 isturned ON, nd12 b becomes a low level (vdd). As a result, MP11 is turnedON and nd12 becomes a high level (vcc). At this time, MP13 and MP14 arealways in an ON state. These MISFETs MP13 and MP14 are used for thepurpose of suppressing an electric current, so as to make a transitionto a low level at high speed at the time of signal level conversion.MP13 and MP14 can be omitted if a desired performance can be obtainedwithout these MISFETs. In this case, an area reduction effect can beachieved.

As described above, the operation of the level conversion circuit isdefined.

Two signals whose signal amplitude is converted by the level upconverter LSC are buffered by the pre-buffer PBF to a driving forcesufficient to drive the main buffer MBF at the last stage. At this time,since nd11 is at a high level (vcc_25), nd15 is at a high level(vcc_25). On the other hand, since nd12 is at a low level (vdd), nd16becomes a high level (vcc). These outputs from the pre-buffer PBF areinputted to the main buffer MBF. In the main buffer MBF, since nd15 isat a high level, MN16 is turned ON and MP6 is turned OFF. Therefore,since nd13 becomes a vssc potential and the gate potential of MN5 is atvcc_25, MN5 is also turned ON. On the other hand, since nd16 is at ahigh level (vcc), MP13 is turned OFF and MN6 is turned ON. Therefore,since nd14 is at a vdd potential and the gate potential of MP5 is atvdd, MP5 is also in an OFF state. Consequently, the output o is at avssc level.

FIG. 15 is an operational waveform diagram of main nodes in the I/Ocircuitry of FIG. 14.

Next, the withstand voltage mitigation will be described.

The MISFETs MN1 to MN6 and MP1 to MP6 shown in FIG. 14 form a withstandvoltage mitigation mechanism. When the gate voltage of MN1 is at a lowlevel, MP1 is turned ON, and the source side of MN1 becomes vdd. Avoltage relation at this time will be shown.

As for MN7, the gate voltage is vss, the source voltage is vss, and thedrain voltage is vdd. Therefore, MN7 is within the maximum appliedvoltage of a MISFET having a thin gate insulating film.

As for MP1, the gate voltage is vss, the source voltage is vdd, and thedrain voltage is vdd. Therefore, MP1 is within the maximum appliedvoltage of a MISFET having a thin gate insulating film.

As for MN1, the gate voltage is vss, the source voltage is vdd, and thedrain voltage is vcc_25. Therefore, MN1 is within the maximum appliedvoltage of a MISFET having a thick gate insulating film. On the otherhand, if the gate voltage of

MN1 is at a high level (vdd), MP1 is turned OFF and the source side ofMN1 becomes vss. A voltage relation at this time will be shown.

As for MN7, the gate voltage is vdd, the source voltage is vss, and thedrain voltage is vss. Therefore, MN7 is within the maximum appliedvoltage of a MISFET having a thin gate insulating film.

As for MP1, the gate voltage is vdd, the source voltage is vdd, and thedrain voltage is vss. Therefore, MP1 is within the maximum appliedvoltage of a MISFET having a thin gate insulating film. As for MN1, thegate voltage is vdd, the source voltage is vss, and the drain voltage isvss. Therefore, MN1 is within the maximum applied voltage of a MISFEThaving a thick gate insulating film.

In this case, a purpose is to suppress the maximum applied voltage ofMN7 below vdd as described above. MN8, MN2, and MP2 have similarfunction, and the maximum applied voltage of MN8 can be suppressed belowvdd. Next, a withstand voltage mitigation mechanism forming LUC_A willbe described.

The case where nd11 is at a low level (vss) will be described.

At this time, as for MN10, the gate voltage is vss, the source voltageis vdd, and the drain voltage is vcc_25. Therefore, MN10 is within themaximum applied voltage of a MISFET having a thick gate insulating film.

As for MP4, the gate voltage is vss, the source voltage is vcc_25, andthe drain voltage is vcc_25. Therefore, MP4 is within the maximumapplied voltage of a MISFET having a thick gate insulating film.

As for MN4, the gate voltage is vcc_25, the source voltage is vcc_25,and the drain voltage is vcc. Therefore, MN4 is within the maximumapplied voltage of a MISFET having a thick gate insulating film.

The case where nd11 is at a high level (vcc_25) will be described.

As for MN10, the gate voltage is vcc_25, the source voltage is vdd, andthe drain voltage is vdd. Therefore, MN10 is within the maximum appliedvoltage of a MISFET having a thick gate insulating film.

As for MP4, the gate voltage is vcc_25, the source voltage is vcc_25,and the drain voltage is vdd. Therefore, MP4 is within the maximumapplied voltage of a MISFET having a thick gate insulating film.

As for MN4, the gate voltage is vcc_25, the source voltage is vdd, andthe drain voltage is vdd. Therefore, MN4 is within the maximum appliedvoltage of a MISFET having a thick gate insulating film.

In this case, a purpose is to suppress the maximum applied voltage ofMN10 below (vcc-vcc_25) as described above. MN9, MN3, and MP3 havesimilar function, and the maximum applied voltage of MN8 can besuppressed below (vcc-vcc_25).

In the foregoing, the I/O circuitry using a MISFET with a high withstandvoltage and operated at high speed with a voltage lower than thewithstand voltage of the MISFET has been described. However, if theoperating speed slower than that of the embodiment shown in FIG. 1 doesnot cause any problem, the level up converter may be changed.

FIG. 16 depicts another embodiment in which a MISFET supposed to beoperated at a vcc power supply voltage is used, but the MISFET isoperated at a lower power supply voltage vcc_18. FIG. 16 shows a levelup converter, and conventional circuits are used for a pre-buffer and amain buffer. In this case, since two types of wiring for power supplyare not required, an effect of reducing design complexity can beachieved.

Next, this circuit (level up converter) will be described. In this levelup converter, MN21, MN22, MP21, MP22, and an inverter INV21 are formedof MISFETs having a thin gate insulating film, and other MN23, MN24,MN25, MN26, MP23, MP24, MP25, MP26 and an inverter INV22 are formed ofMISFETs having a thick gate insulating film to which a vcc power supplyvoltage can be applied.

This circuit is a cross-couple-type level conversion circuit similar toa standard level conversion circuit. A feature of the present embodimentlies in that MP23 and MP24 for current control are formed of MISFETshaving a threshold voltage lower than that of MP25 and MP26, and MN23and MN24 are formed of MISFETs having a threshold voltage lower thanthat of MN25 and MN26. Note that, MN25 and MN26 function as a latch forkeeping the state at the time of cut-off of power supply and performinga stable operation. Since the MISFET having a thick gate insulating filmis designed to be operated at vcc (for example, 3.3 V), if it isoperated at vcc_18 (for example, 1.8 V), the saturation current of theMISFET is decreased. The level up converter achieves signal amplitudeconversion by extracting a current with the MISFETs of MN21 and MN22.Therefore, for example, when an input signal is changed from low tohigh, MP23 is controlled to be OFF, thereby achieving high-speedconversion. Thus, MP23 and MP24 are effective for the purpose oflimiting a current path to the vcc_18 power supply at the time of levelconversion. However, since the MISFET originally designed to be operatedat vcc is operated at the vcc_18 power supply voltage, when the input ibecomes a high level, the driving current for raising the drain of MP23to a vcc_18 power supply voltage level is decreased, and the operationspeed is decreased. For its prevention, by reducing the thresholdvoltage of these MP23 and MP24, the raising to the vcc_18 level can beperformed at high speed. Accordingly, even when the operation powersupply voltage is low, the operation speed of the level up converter canbe increased. The same goes for MN25 and MN26, in which the thresholdvoltage is reduced in order to prevent an operational delay due to theuse of MISFETs having a thick gate insulating film. In the presentembodiment, an N type MISFET in which a vcc_18 power supply voltage isapplied to a gate for the purpose of current control is used at thesource side of each of MN25 and MN26. This MISFET limits the drivingcapability of MN25 and MN26, which makes it possible to achieve ahigh-speed operation of the level conversion circuit. When the gatelength of this MISFET is increased, the threshold value is effectivelyincreased, and thus, a current suppression effect is also increased.This N type MISFET is not imperative, and if a desired performance issatisfied without this N type MISFET, the design without this N typeMISFET is possible. In that case, an area reduction effect can beachieved, for example.

Hereinafter, the case where the I/O circuitry driven by a voltage higherthan a power supply voltage for use in an interface according to thepresent invention is applied to SSTL will be described.

FIG. 17 depicts one embodiment of an input circuit satisfyingspecifications of SSTL2 standards of 1.8 V. In the SSTL2 standards of1.8 V, an input signal is not delivered as a so-called full-amplitudesignal which makes a transition exactly between 0 V and vcc_18 butdelivered as a signal having the maximum amplitude of smaller than 1.8V, where a half voltage of vcc_18 is set to be the center of theamplitude as a reference voltage (VREF) (if vcc_18 is 1.8 V, VREF=0.9V). A feature of the present embodiment lies in that a differentialamplifier SA is provided at an input, and a power supply of thisdifferential amplifier SA is driven by a vcc power supply. Accordingly,even when a transistor to which a vcc power supply voltage is supposedto be applied is used, a signal having an amplitude of 1.8 V, which is alow voltage, can be stably amplified at high speed, and a high-qualitysignal can be delivered to the subsequent stage. An output of thedifferential amplifier SA is inputted to an input buffer IBF as afull-amplitude signal and then delivered through a level conversioncircuit to an internal logic.

Note that, when the vdd voltage is low, for example, 1 V, vdd can beused as VREF. In this circuit, all ground levels are at a ground powersupply voltage vss, which is used in the internal logic circuit. This isbecause a large noise on a power supply line generated by an outputbuffer is cut off at the input circuit side.

FIG. 18 is a drawing of a circuit example of the differential amplifierSA shown in FIG. 17. In FIG. 18, the differential amplifier SA uses adifferential-type amplifier. A feature of this circuit lies in that,when a power supply level of an input signal is 1.8 V, the power supplyof a sense amplifier receiving the input signal is operated not at 1.8 Vbut at a high voltage of 3.3 V, thereby providing a circuit that stablyoperates at high speed by using a transistor optimized for 3.3 V. Thedifferential amplifier SA shown in this embodiment shows an example of ageneral differential-type operational amplifier. Since the input signallevel of this circuit and the voltage level of VREF (vcc_18/2=0.9 V) arelow, a method in which a voltage is sensed at a P type MISFET is taken.This is because, since the gate voltage is as low as about 1 V, byincreasing the source-drain voltage and the source-gate voltage of the Ptype MISFET to 3.3 V, the transistor can be operated in a so-calledsaturation area of the transistor.

In view of a circuitry characteristic of the differential amplifier SAbeing a current-amplifying-type amplifier, it is necessary that acurrent always flows through this differential amplifier SA so as tosense the voltage level. For the reduction of power consumption, thiscurrent is required to be eliminated at the time of non-operation. Forits achievement, the current-control P type MISFET of the senseamplifier is turned OFF by setting a control signal CTL at a low level,thereby cutting off the current flowing through the operationalamplifier. At this time, since an output O1 of the sense amplifier is ina floating state, there is the possibility that a through current occursin a circuit at a subsequent stage. Therefore, by setting the CTL signalto low, an output of a NAND circuit is fixed to high, which can preventsuch a through current in this NAND circuit.

FIG. 19 depicts another embodiment of the input circuit shown in FIG.16. This circuit is formed in order to improve the gain and offsetcharacteristics of the operational amplifier by applying a bias voltageto the gate of a current-control P type MISFET MP30 of the operationalamplifier. Normally, in a standard operational amplifier, the voltagegenerated from a bias generating circuit is applied to the P typeMISFET. In the I/O circuitry, however, such a bias generating circuit isdifficult to provide in some cases. In that case, in view of the factthat a node ND30 in the operational amplifier can serve as some sort ofbias generating circuit, its voltage can be used as a bias voltage. Alsoin this circuit, unnecessary current consumption has to be suppressed atthe time of non-operation, and therefore, it is necessary to performcurrent consumption reduction control by the use of a control signalCTL. By setting the control signal CTL to low, a transmission gateformed of MN33 and MP33 is turned OFF, and gates of ND30 and MP30 arecut off. Simultaneously, since a P type MISFET of MP37 is turned ON, thegate voltage of MP30 becomes vcc, and the power supply of theoperational amplifier is cut off. At this time, in association with thecut-off of the power supply of the operational amplifier, an output ofthe operational amplifier becomes unstable. However, since MN32 isturned ON at this time, a through current can be avoided in a circuit ata subsequent stage. In FIG. 19, sending a high signal to an internalcircuit to stop the operational amplifier is controlled with this CTLsignal.

FIG. 20 depicts operational waveforms of the circuit shown in FIG. 17.An input level of SSTL18 is not the signal with a full amplitude of 1.8V but the signal with an amplitude of about 0.4 to 1 V centering onVREF. In this case, VREF is defined by specifications to be half thevoltage of the vcc_18 power supply. First, a transition from a low levelto a high level will be described. When an input is changed at a time T1from a low level to a high level, the input signal crosses VREF at thetime T1, and therefore, the output of the sense amplifier is changed.The sense amplifier then amplifies a difference between the input signalI and VREF and converts it to a signal with an amplitude of 0 V and vcc.It is assumed here that an input buffer receiving an output from thesense amplifier at the time T2 performs wave shaping. Then, the signalis converted by the level conversion circuit to a signal with anamplitude of vdd, and then makes a transition at a time T3 to a highlevel.

Next, a transition from a high level to a low level will be described.When the input is changed at a time T4 from a high level to a low level,the input signal crosses VREF at the time T4, and therefore, an outputof the sense amplifier is changed. The sense amplifier then amplifies adifference between the input signal I and VREF and converts it to asignal with an amplitude of 0 V and vcc. It is assumed here that theinput buffer receiving an output from the sense amplifier at the time T5performs wave shaping. Then, the signal is converted by the levelconversion circuit to a signal with an amplitude of vdd, and is thenchanged to 0 V at a time T6.

FIG. 21 is a drawing that depicts one embodiment of a terminatingresistor of the input circuit. In this case, the terminating resistor isformed of MP40 and MN40 in an ESD circuit. These MISFETs are placedbetween an input I and a VTT power supply. The VTT power supply is setto have a value of vcc_18/2 in SSTL, for example. Gate signals of theseMISFETs are connected to CTL1 at the P type MISFET side and to CTL2 atthe N type MISFET, respectively. CTL1 and CTL2 are formed by usingMISFETs that can withstand the application of a vcc voltage, and thesesignals are driven at a vcc power supply voltage. When MN40 is formed tohave a structure as described above, since MN40 can be used at a placewhere an ON resistance of the transistor is small, it is possible toachieve an area reduction effect. For example, when the terminatingresistor is set to 50 Ω at the time of driving at 1.8 V, if it isassumed that the ON resistance of the MISFET is 2.5 KΩ per unit width (1micrometer), a MISFET of 50 μm is required. By contrast, at the time ofdriving at 3.3 V, if it is assumed that the ON resistance of the MISFETis 1 KΩ per unit width, a MISFET required is of 20 μm. As describedabove, a size reduction of the MISFET can be achieved, and resultingarea reduction can be achieved. Furthermore, since the control voltageof CTL1 and CTL2 is high, a sufficiently high gate voltage can beapplied particularly in the case of controlling an N type MISFET.Therefore, since such an N type MISFET can be operated in a sufficientsaturation area, it is possible to sufficiently reduce an influence ofslight fluctuations of the control voltage on variations in ONresistance.

Note that the P type MISFETs can be omitted in this case, and theterminating resistor can be formed of only N type MISFETs.

In the present embodiment, description has been made mainly to SSTL.However, the present embodiment can be applied to a terminatingtransistor of a general low-amplitude l/O.

In the foregoing, the invention made by the inventors of the presentinvention has been concretely described based on the embodiments.However, it is needless to say that the present invention is not limitedto the foregoing embodiments and various modifications and alterationscan be made within the scope of the present invention.

The present invention can be applied to a semiconductor device such as asystem LSI or a microprocessor for mobile devices.

1-16. (canceled)
 17. A semiconductor integrated circuit devicecomprising: a first circuit that outputs a first signal which variesbetween a ground voltage and a second voltage higher than the groundvoltage; a first conversion circuit that receives the first signal andthat outputs a second signal which varies between the ground voltage anda third voltage higher than the second voltage; a first output circuitthat receives the second signal and that outputs a third signal whichvaries between the ground voltage and a fourth voltage between thesecond voltage and third voltage; a second circuit that outputs a fourthsignal which varies between the ground voltage and the second voltage; asecond conversion circuit that receives the fourth signal and thatoutputs a fifth signal which varies between the ground voltage and thethird voltage; and a second output circuit that receives the fifthsignal and that outputs a sixth signal which varies between the groundvoltage and a fifth voltage between the second voltage and fourthvoltage, wherein the first and second circuits are supplied with theground voltage and the second voltage, wherein the first and secondconversion circuits are supplied with the ground voltage and the thirdvoltage, wherein the first output circuit is supplied with the groundvoltage and the fourth voltage, and wherein the second output circuit issupplied with the ground voltage and the fifth voltage.
 18. Thesemiconductor integrated circuit device according to claim 17, whereineach said first and second circuits includes a first field-effecttransistor that is supplied with the ground voltage and the secondvoltage, and wherein each said first and second conversion circuits andeach said first and second output circuits include a second field-effecttransistor having a gate insulating film thicker than a gate insulatingfilm of said first field effect transistor and that is supplied with thethird voltage.
 19. A semiconductor integrated circuit device comprising:a first circuit that outputs a first signal which varies between aground voltage and a second voltage higher than the ground voltage; afirst conversion circuit that receives the first signal and that outputsa second signal which varies between the ground voltage and a thirdvoltage higher than the second voltage; a first output circuit thatreceives the second signal and that outputs a third signal which variesbetween the ground voltage and a fourth voltage between the secondvoltage and third voltage; a second circuit that outputs a fourth signalwhich varies between the ground voltage and the second voltage; a secondconversion circuit that receives the fourth signal and that outputs afifth signal which varies between the ground voltage and the thirdvoltage; and a second output circuit that receives the fifth signal andthat outputs a sixth signal which varies between the ground voltage andthe third voltage, wherein the first and second circuits are suppliedwith the ground voltage and the second voltage, wherein the first andsecond conversion circuits and the second output circuit are suppliedwith the ground voltage and the third voltage, and wherein the firstoutput circuit is supplied with the ground voltage and the fourthvoltage.
 20. The semiconductor integrated circuit device according toclaim 19, wherein each said first and second circuits include a firstfield-effect transistor that is supplied with the second voltage, andwherein each said first and second conversion circuits and each saidfirst and second output circuits include a second field-effecttransistor having a gate insulating film thicker than a gate insulatingfilm of said first field effect transistor and supplied with the thirdvoltage.